Molecular chaperones are key players in the maintenance of a healthy proteome and in homeostasis of the cell. Dysregulation in the function of molecular chaperones leads to many metabolic, oncological, neurodegenerative, and cardiovascular diseases. The Hsp90 chaperoning machine, in particular, involves a number of chaperones and co-chaperones that, through a complex network of interactions, ensure the folding and the functionality of many key regulatory proteins. Current information suggests that targeting this machine may have a significant and combinatorial impact on dysfunctional circuitries that underlie human diseases such as cancer and neurodegenerative diseases. Novel small-molecule compounds that target the Hsp90 machine in a selective manner are needed. They will provide tools and molecular probes to further dissect the biology of this machine to better understand its role in disease etiology and progression, and to facilitate the subsequent development of therapeutics against relevant targets. This application aims to develop a high- throughput assay based on progesterone and glucocorticoid receptors, which are physiological clients of Hsp90, and the core components of the Hsp90 chaperoning machine (Hsp90, Hsp70, Hsp40, Hop, and p23). This assay would significantly enhance the discovery of chemical probes that would affect the functional core of the Hsp90 machine. It would also provide the long sought-after screening tool for specific inhibitors of Hsp90 alpha and beta isoforms and facilitate the identification of molecular targets of active compounds.